Gas-barrier resins of a variety of kinds have heretofore been used as represented, particularly, by polyvinylidene chloride, polyacrylonitrile and ethylene/vinyl alcohol copolymer. However, use of the polyvinylidene chloride and polyacrylonitrile has been limited from the standpoint of their environmental problems while the ethylene/vinyl alcohol copolymer is accompanied by such a problem that the gas-barrier property thereof is much dependent upon the humidity and is subject to decrease under highly humid conditions.
As a method of imparting gas-barrier property to the packing materials, there has been known to use a film obtained by vacuum-evaporating an inorganic matter on the surface of a base material. However, the film of this kind is very expensive. Besides, the vacuum-evaporated film has a problem in regard to flexibility and poor adhesion to other resin layers.
To solve the above problems, there have been proposed a gas-barrier film obtained by forming, on a base material, a film which comprises high molecules A in the form of an aqueous solution, water-soluble or water-dispersing high molecules B and an inorganic layer compound (JP-A-9-151264), a gas-barrier film obtained by applying a layer containing a metal compound onto the surface of a layer of a formed article of a mixture of a polymer of the type of a poly(metha)acrylic acid and polyalcohols (JP-A-2000-931), and a gas-barrier coating material containing a polyvinyl alcohol, an ethylene/maleic acid copolymer and a metal compound having a valency of two or more (JP-A-2004-115776).